Recently I came across an article proposing a practice of 4 Step to help you let go of negative thoughts. You can find the full article at 4 Steps to Freedom from Negative Thinking. Here are the 4 steps in brief, which it is suggested you carry out when you experience a negative thought:
1. Name the type of negative thought you are experiencing (e.g. catastrophising about what might happen).
2. Recognise how you are feeling with the thought in your mind.
3. Release the thought by saying to your self a simple phrase such as 'Breathing in I acknowledge the feeling that's here; breathing out, I release it.'
4. Redirect your thought - Focus on something else that is healthier or more important.
For an eBook Guide to Dealing with Negative Thoughts, see:
CBT Techniques to Beat Negative Thinking